This invention relates to biodegradable high performance hydrocarbon base oils, suitable as engine oil and industrial oil compositions. In particular, it relates to lubricant base oil compositions, and process for making such compositions by the hydroisomerization/hydrocracking of paraffinic waxes, suitably Fischer-Tropsch waxes.
It is well known that very large amounts of lubricating oils, e.g., engine oils, transmission oils, gear box oils, etc., find their way into the natural environment, accidentally and even deliberately. These oils are capable of causing much environmental harm unless they are acceptably biodegradable. For this reason there is increasing emphasis in this country, and abroad, to develop and employ high performance lubricant base oils which are environmentally friendly, or substantially biodegradable on escape or release into the environment.
Few hydrocarbon base oils are environmentally friendly though their qualities as lubricants may be unchallenged. The literature stresses the superior biodegradability of ester based lubricants, natural and synthetic, over hydrocarbon based products. However there is little or no emphasis on performance. Few references are found relating to the biodegradability of hydrocarbon lubricants. Ethyl Petroleum Additives""s EP 468 109A however does disclose the biodegradability of lubricating oils containing at least 10 volume percent of a xe2x80x9cbiodegradable liquid hydrocarbon of lubricating viscosity formed by oligomerization of a 1-alkene hydrocarbon having 6 to 20 carbon atoms in the molecule and hydrogenation of the resultant oligomer.xe2x80x9d Apparently hydrogenated oligomers of this type have unexpectedly high biodegradability, particularly those having at least 50 volume percent dimer, trimer and/or tetramer. Ethyl Petroleum Additive""s EP 558 835 A1 discloses lubricating oils having similar polyalphaolefin, PAO, components. However, both references point out performance debits for the synthetic and natural ester oils, such as low oxidative stability at high temperatures and poor hydrolytic stability. British Petroleum""s FR 2675812 discloses the production of biodegradable PAO hydrocarbons base oils by dewaxing a hydrocracked base oil at low temperatures.
There is a clear need for biodegradable high performance hydrocarbon base oils useful as engine oil and industrial oil, or lubricant compositions which are at least equivalent to the polyalphaolefins in quality, but have the distinct advantage of being more biodegradable.
This invention, which supplies these and other needs, accordingly relates to biodegradable high performance paraffinic lubricant base oils, and process for the production of such compositions by the hydrocracking and hydroisomerization of paraffinic, or waxy hydrocarbon feeds, especially Fischer-Tropsch waxes or reaction products, all or at least a portion of which boils above 700xc2x0 F., i.e., 700xc2x0 F.+. The waxy feed is first contacted, with hydrogen, over a dual functional catalyst to produce hydroisomerization and hydrocracking reactions sufficient to convert at least about 20 percent to about 50 percent, preferably from about 20 percent to about 40 percent, on a once through basis based on the weight of the 700xc2x0 F.+ feed, or 700xc2x0 F.+ feed component, to 700xc2x0 F.xe2x88x92 materials, and produce 700xc2x0 F.+ materials rich in methyl-paraffins. This resultant crude product, which contains both 700xc2x0 F.xe2x88x92 and 700xc2x0 F.+ materials, characterized generally as a C5-1050xc2x0 F.+ crude fraction, is first topped via atmospheric distillation to produce a lower boiling fraction the upper end of which boils between about 650xc2x0 F. and 750xc2x0 F., e.g., 700xc2x0 F., and a higher boiling, or bottoms fraction having an initial boiling point ranging between about 650xc2x0 F. and 750xc2x0 F., e.g., 700xc2x0 F., and an upper end or final boiling point of about 1050xc2x0 F.+, e.g., a 700xc2x0 F.+ fraction. The lower boiling fraction, e.g., the 700xc2x0 F.xe2x88x92 fraction, from the distillation is a non-lube, or fuel fraction.
At these conversion levels, the hydroisomerization/hydrocracking reactions convert a significant amount of the waxy, or paraffinic feed to 700xc2x0 F.+ methyl-paraffins, i.e., isoparaffins containing one or more methyl groups in the molecule, with minimal formation of branches of carbon number greater than 1; i.e., ethyl, propyl, butyl or the like. The 700xc2x0 F.+ bottoms fractions so-treated contain 700xc2x0 F.+ isoparaffins that have less than about 7.5 methyl branches per 100 carbon atoms or 6.0 to 7.5 methyl branches, preferably less than about 7.0 methyl branches or 6.0 to 7.0 methyl branches, more preferably from about 6.5 to about 7.0 methyl branches per 100 carbon atoms, in the molecule. These isoparaffins, contained in a mixture with other materials, provide a product from which high performance, highly biodegradable lube oils can be obtained. The degree of branching, particularly methyl branching, is indicative of the biodegradability of the oil. That is, higher degrees of branching are less biodegradable or not biodegradable at all, while lower degrees of branching, e.g.,  less than 7.8 methyls, are indicative of biodegradability.
The higher boiling bottoms fractions, e.g., the 700xc2x0 F.+ bottoms fraction containing the methyl-paraffins, or crude fraction, is dewaxed in a conventional solvent dewaxing step to remove n-paraffins, and the recovered dewaxed product, or dewaxed oil, is fractionated under vacuum to produce paraffinic lubricating oil fractions of different viscosity grades, including hydrocarbon oil fractions suitable as high performance engine oils and engine lubricants which, unlike most hydrocarbon base oils, are biodegradable on release or escape into the environment. In terms of their performance they are unsurpassed by the PAO lubricants, and are superior thereto in terms of their biodegradability.
The feed materials that are isomerized to produce the lube base stocks, and lubricants with the catalyst of this invention are waxy feeds, i.e., C5+, preferably having an initial boiling point above about 350xc2x0 F. (117xc2x0 C.), more preferably above about 550xc2x0 F. (288xc2x0 C.), and contain a major amount of components boiling above 700xc2x0 F. (370xc2x0 C.). The feed may be obtained either from a Fischer-Tropsch process which produces substantially normal paraffins, or from petroleum derived slack waxes.
Slack waxes are the by-products of dewaxing operations where a diluent such as propane or a ketone (e.g., methylethyl ketone, methyl isobutyl ketone) or other diluent is employed to promote wax crystal growth, the wax being removed from the base oil by filtration or other suitable means. The slack waxes are generally paraffinic in nature, boil above about 600xc2x0 F. (316xc2x0 C.), preferably in the range of 600xc2x0 F. (316xc2x0 C.) to about 1050xc2x0 F. (566xc2x0 C.), and may contain from about 1 to about 35 wt. % oil. Waxes with low oil contents, e.g., 5-20 wt. % are preferred; however, waxy distillates or raffinates containing 5-45% wax may also be used as feeds. Slack waxes are usually freed of polynuclear aromatics and hetero-atom compounds by techniques known in the art; e.g., mild hydrotreating as described in U.S. Pat. No. 4,900,707, which also reduces sulfur and nitrogen levels preferably to less than 5 ppm and less than 2 ppm, respectively. Fischer-Tropsch waxes are preferred feed materials, having negligible amounts of aromatics, sulfur and nitrogen compounds. The Fischer-Tropsch liquid, or wax, is characterized as the product of a Fischer-Tropsch process wherein a synthetic gas, or mixture of hydrogen and carbon monoxide, is processed at elevated temperature over a supported catalyst comprised of a Group VIII metal, or metals, of the Periodic Table of The Elements (Sargent-Welch Scientific Company, Copyright 1968), e.g., cobalt, ruthenium, iron, etc. The Fischer-Tropsch wax contains C5+, preferably C10+, more preferably C20+ paraffins. A distillation showing the fractional make up (xc2x110 wt. % for each fraction) of a typical Fischer-Tropsch process liquid feedstock is as follows:
The wax feed is contacted, with hydrogen, at hydrocracking/hydroisomerization conditions over a bifunctional catalyst, or catalyst containing a metal, or metals, hydrogenation component and an acidic oxide support component active in producing both hydrocracking and hydroisomerization reactions. Preferably, a fixed bed of the catalyst is contacted with the feed at conditions which convert about 20 to 50 wt. %, preferably about 25 to 40 wt. %, of the 700xc2x0 F. components of the feed to 700xc2x0 F.xe2x88x92 materials and produce a lower boiling fraction having an upper end boiling point between about 650xc2x0 F. and 750xc2x0 F., e.g., 700xc2x0 F., and a higher boiling, or bottoms fraction having an initial boiling point between about 650xc2x0 F. and 750xc2x0 F., e.g., 700xc2x0 F., the higher boiling fraction that remains containing high quality blending components for the production of high performance biodegradable base oils. In general, the hydrocracking/hydroisomerization reaction is conducted by contacting the waxy feed over the catalyst at a controlled combination of conditions which produce these levels of conversion; i.e., by selection of temperatures ranging from about 400xc2x0 F. to about 850xc2x0 F., preferably from about 500xc2x0 F. to about 700xc2x0 F., pressures ranging generally from about 100 pounds per square inch gauge (psig) to about 1500 psig, preferably from about 300 psig to about 1000 psig, hydrogen treat gas rates ranging from about 1000 SCFB to about 10,000 SCFB, preferably from about 2000 SCFB to about 5000 SCFB, and space velocities ranging generally from about 0.5 LHSV to about 10 LHSV, preferably from about 0.5 LHSV to about 2.0 LHSV.
The active metal component of the catalyst is preferably a Group VIII metal, or metals, essentially free of noble metal or metals, of the Periodic Table Of The Elements (Sargent-Welch Scientific Company Copyright 1968) in amount sufficient to be catalytically active for hydrocracking and hydroisomerization of the waxy feed. The catalyst preferably also contains, in addition to the Group VIII metal, or metals, a Group VIB metal, or metals, of the Periodic Table, and may also contain a Group IB metal or metals. Generally, metal concentrations range from about 0.01 percent to about 20 percent, based on the total weight of the catalyst (wt. %), preferably from about 0.5 wt. percent to about 20 wt. percent. Exemplary of such metals are such non-noble Group VIII metals as nickel and cobalt, or mixtures of these metals with each other or with other metals, such as copper, a Group IB metal, or molybdenum, a Group VIB metal. The metal, or metals, is incorporated with the support component of the catalyst by known methods, e.g., by impregnation of the support with a solution of a suitable salt or acid of the metal, or metals, drying and calcination. Preferred catalysts contain cobalt and molybdenum, and copper or nickel may also be present, but nickel seems to have little effect on the hydroisomerization.
The catalyst support is constituted of metal oxide, or metal oxides, components at least one component of which is an acidic oxide active in producing olefin cracking and hydroisomerization reactions. Exemplary oxides include silica, silica-alumina, clays, e.g., pillared clays, magnesia, titania, zirconia, halides, e.g., chlorided alumina, and the like. The catalyst support is preferably constituted of silica and alumina, a particularly preferred support being constituted of up to about 35 wt. % silica, preferably from about 2 wt. % to about 35 wt. % silica, and having the following pore-structural characteristics:
The base silica and alumina materials can be, e.g., soluble silica containing compounds such as alkali metal silicates (preferably where Na2O:SiO2=1:2 to 1:4), tetraalkoxy silane, orthosilic acid ester, etc.; sulfates, nitrates, or chlorides of aluminum alkali metal aluminates; or inorganic or organic salts of alkoxides or the like. When precipitating the hydrates of silica or alumina from a solution of such starting materials, a suitable acid or base is added and the pH is set within a range of about 6.0 to 11.0. Precipitation and aging are carried out, with heating, by adding an acid or base under reflux to prevent evaporation of the treating liquid and change of pH. The remainder of the support producing process is the same as those commonly employed, including filtering, drying and calcination of the support material. The support may also contain small amounts, e.g., 1-30 wt. %, of materials such as magnesia, titania, zirconia, hafnia, or the like.
Support materials and their preparation are described more fully in U.S. Pat. No. 3,843,509 incorporated herein by reference. The support materials generally have a surface area ranging from about 180-400 m2/g, preferably 230-375 m2/g, a pore volume generally of about 0.3 to 1.0 ml/g, preferably about 0.5 to 0.95 ml/g, bulk density of generally about 0.5-1.0 g/ml, and a side crushing strength of about 0.8 to 3.5 kg/mm.
The hydrocracking/hydroisomerization reaction is conducted in one or a plurality of reactors connected in series, generally from about 1 to about 5 reactors; but preferably the reaction is conducted in a single reactor. The waxy hydrocarbon feed, e.g., Fischer-Tropsch wax, preferably one boiling above about 700xc2x0 F., or has a large amount of 700xc2x0 F.+ hydrocarbon components, is fed, with hydrogen, into the reactor, a first reactor of the series, to contact a fixed bed of the catalyst at hydrocracking/hydroisomerization reaction conditions to hydrocrack, hydroisomerize and convert at least a portion of the waxy feed to products which include after further work up high quality oils and lube blending components.